If you look for a truly in-memory open source database then VoltDB might be the only choice available at the moment. Unfortunately, for me, there are no binaries for Windows available as big part of the code was written in C/C++ which is hard to port from Linux to Windows. But there is a way to run VoltDB when your main operating system is Windows. A solution provided on www.VoltDB.com is to use Docker Toolbox. But the description they provide seems to be a bit outdated, i.e., it did not work for me.

There were three things I had to do in order to have it work. The whole procedure looked like this: